Fuel burner control system



Oct. 12, 1943 s. M. MILLER 2,331,712

BURNER CONTROL SYSTEM Filed July 14, 1941 &

INVENTOR Ernzsl M. Mi11r- ATTORNEY Patented Oct. 12, 1943 2,331,712 FUELBURNER CONTROL SYSTEM Ernest M. Miller, Excelsior, Minn., asslgnor toMinneapolis-Honeywell Regulator Company, Minneapolis, Minn, acorporation of Delaware Application July 14, 1941, Serial No. 402,301

Claims.

The present invention is directed broadly to systems for automaticallycontrolling fuel burners and is more particularly concerned withsysterms which have a timed trial ignition period and a device fordetecting the presence or absence of combustion, and which are of thesocalled non-recycling type on flame failure.

It is old in the prior art in connection with fluid fuel burners, suchas oil burners, to provide an automatic control system in which athermal safety switch times the trial ignition period. That is, on acall for heat by the thermostat in control of the system, the burnermotor and ignition device as well as the heater for the safety switchare energized. If combustion is established within a predetermined timethe safety switch heater is effectively deenergized and the burner motorremains energized, but if combus-- tion is not established the safetyswitch is opened paragraph, which will reenergize the safety switchheater and shut the system down upon a flame failure following thesuccessful establishment of combustion and not allow the burner motor tobe re-energized without a manual operation. Ordinarily the safety switchwould have the same timing upon a flame failure as upon an originalfailure to establish combustion (usually about 90 seconds) which meansthat following a flame failure and a reenergization of the safety switchheater by the combustion responsive switch, the burner'motorwould'remain energized and would pump raw fuel into the combustionchamber of the furnace for 90 seconds. In order to eliminate thisdisadvantage I materially reduce the timing of the safety switchfollowing a flame failure.

It is therefore a prime object of this invention to connect the heaterfor the thermal safety switch in series with an electrical impedance,such as a relay winding, upon an original call for heat and to connectit directly across the source of power to materially reduce the safetyswitch timing upon a flame failure following the successfulestablishment of combustion.

It is a further object, where a relay winding is used, to control anignition device with the relay, thus providing an intermittent ignitionsystem.

These and other objects will readily become apparent as the followingspecification is read in the light of the accompanying drawing, thesingle time of which schematically illustrates element II fixed at oneend and carrying at its free end a pair of resilient contact blades I2and i3 which cooperate respectively with the stationary contacts i4 andIS. The stationary contacts are so adjusted that on a decrease intemperature the contact blade I! will first engage contact l4,-and thenat a slightly lower temperature the contact blade l3 will engagestationary contact Indicated generally at H isa thermally timed safetyswitch comprising a bimetallic blade I8 'reset member indicated at 22.

fixed at its lower end and cooperating at its upper end with a pair ofresilient contact blades l9 and 20 which are biased open butwhich arelatched in closed position by means of the blade l8 when it is -in itscold position as shown in the drawing. Indicated at 2| is an electricheater for heating the thermal blade l8 and causing it to warp asindicated by the arrow in the drawing. After it has been heated for apredetermined period of time, it will move from beneath the switch blade2b and permit the blades l9 and 20 to move to open circuit positionunder the influence of their bias. The opening of this safety switchdeenergizes the heater 2| thereby cooling the thermal blade Ill. Theswitch cannot be reclosed automatically by the blade but must be resetmanually by means of the trip-free As the member 22 is raised, bothblades l9 and 20 are raised andthe thermal blade I8 is permitted toreturn to its cold position. It will be noted that the long legIndicated generally at 25 is a conventional type of two wire, closedcold combustion switch. This switch is shown as comprising a movableswitch blade 26 and a stationary contact 21. The blade 26 is intended tobe moved by means of a combustion responsive device which may take theform of a thermal element responding either directly to radiant heat ofthe combustion chamber or it may be mounted inthe stack and respond tothe temperature of the products of combustion. It is usual practicetointerpose a slip friction connection between the thermal element andthe blade 26 to provide for the blade being actuated immediately upon areversal of temperature change so that the operation of the switch willbe responsive immediately to the appearance or disappearance ofcombustion within the furnace and will not be dependent for operationupon the attainment of any predetermined temperature at the thermalelement.

A relay winding is indicated at 36 for controlling an armature 3| whichin turn actuates a series of switch arms 32, 33, 34, 35 and 36. Switcharm 34 cooperates with an out contact 31 and the switch arms 32, 33, 35and 36 cooperate with in contacts 38, 39, 46 and 4|, respectively.

Relay winding 44 -is adapted to control armature 45 which in turnactuates the switch arms 46, 41, 48 and 49. The switch arm 46 cooperateswith out contact 56 and the switch arms 41, 48 and 46 cooperate with incontacts -5|, 52, 53, respectively,

This system controls the usual oil burner motor 55 which when energizeddelivers oil to a combustion chamber for establishing combustiontherein. The usual ignition device 56 is provided for igniting the oil,

Electrical power for operating the system is supplied from the two linewires 63 and 6|. The low voltage portion of the system is fed from thesecondary winding 62 of a stepdown transformer indicated at 63, saidtransformer being provided with the usual primary winding 64 connectedacross the line wires 66 and 6| by means of conductors 65 and 66.

Operation The parts are shown in the drawing in the position which theywill assume when the room thermostat I6 is satisfied and the two switch26, contact 21, conductor 15,.heater 2|, conductors 16 and 11, switchblades 26 and i9, and conductor 18 back to the other side of secondarywinding 62. This circuit therefore electrically connects relay winding36 and electric heater 2|,

35 and 36 to move into engagement with theirv stationary contacts 36,39, 46 and 4|, respectively. The movement of the contact arms 35 and 36into engagement with their stationary contact establishes a circuit fromthe line wire 66 through conductors 66 and 8|, stationary contact 46,switch arm 35, conductor 62, switch arm 36, stationary contact 4|,conductor 63, ignition device 56, and conductors 64 and 35 back to theother line wire 6|. This circuit renders the ignition device operative.

The operation of the switch arm 34 from the stationary contact 31 has noeflect on the system inasmuch as no circuit was passing therethrough.The engagement of the contact arm 32 with its stationary contact 36establishes a holding cir-' cuit for the relay winding 36 whichisindependent of switch blade l3 and stationary contact II. This circuitmay be traced from one side of the secondary winding 62 throughconductor 13, stationary contact |4, switch blade l2, bimetallic elementconductors 61 and 66, stationary con-- tact 36, switch arm 32,conductors 33 and 13, relay winding 36, conductor 14, switch arm 23,contact 21, conductor 15, electric .heater 2|, conductors 1.6 and 11,switch blades 26 and |6,-and conductor 16 back to the other side of thesecondary winding 62. The purpose of this circuit is merely to establisha more reliable circuit forthe relay winding 36 in-view of the fact thatcontact between the switch blade l3 and contact I5 is never very firmand this switch is apt to chatter. Inasmuch as the circuit between theswitch blade l2 and the contact I4 is made first, this contact will befirm and may be depended upon' to hold in the relay 36.

Engagement of the switch arm 33 with its conblades l2 and I3 aretherefore out of engage- 5o tact 33 results in the energization of relaywindment with their respective stationary contacts l4 and I5. At thistime both of the relay windings 36 and 44 will be deenergized as will bethe oil burner motor 35 and the ignition device 36.

There will be no combustion present in the furnace and therefore thecombustion responsive switch-will be in closed position. 'Ifhesatetyswitch thermal blade l6 will be in its cold position as shown, holdingthe contact blades l3 and 26 closed.

, As a result of the 'above condition, the temductor 16, stationarycontact l4, switch blades V I2 and I3, stationary contact l5, conductor1|, out contact 56, switch arm 46, conductors 12 and ing 44. Thiscircuit may be traced from one side of the secondary winding 32 throughconductor 16, contact l4, switch blade l2, bimetallic element conductors61 and 33, contact 33, switch arm 32, conductor 36, switch arm 33,contact 36, con-.

ductors 3|, 62 and 33, relay winding 44, conductors 64 and 11, switchblades." and I3, and conductor 13 back to the other side of thesecondary winding 32. I

Energization of this relay winding 44 results in the movement of switcharm 43 out of engagement with its stationary contact 33. This breaks theoriginal circuit through which the relay winding 36 was energized, butit will be noted that the holding circuit for the relay winding 36 isindependent of switch arm 43 and therefore relay winding 36 remainsenergized. Movement 01' switch arm 41 into engagement with itsstationary'contact 5| sets up' a holding circuit for the relay winding44 which is independent of the switch arms 32 and 33 under the controloi relay winding 36. This holding circuit may be traced from one side ofthe secondary winding 32' through conductor 16, contact l4, switch blade13, relay winding 36, conductor 14, switch arm I2, bimetallic elementconductors 31 and 33,

' of the system.

switch arm.4|, contact conductors 91 and 93, relay winding 44,conductors 94 and I1, switch blades 29 and I9, and conductor 13 back tothe other side of the secondary winding 52.." It will therefore be seenthat at this time the relay winding 44 is held in through the switchblade l2 on the room thermostat l9 and its stationary contact I4 and isindependent of the action of the relay winding 39 and the combustion stch 25.

Energization of the relay winding 44 a 0 results in rendering the burnermotor 55 operative. The

circuit for accomplishing this may be traced fromthe line wire 59through conductors 39 and 99, contact 52, switch arm 48, conductor I99,switch arm 49, contact 53, conductor |9|, burner motor 55, andconductors I92 and 35 back to the other line wire 52. It will beappreciated that as soon its armature 3| that it will energize the relaywinding 44 which will immediately pull in its armature 45. Therefore thetwo armatures 3| and 45 will be pulled in substantially simultaneouslywhich will result in the substantial simultaneous energization of theignition device 55 and the burner motor 55, although actually theignition device will be energized a fraction of a second before theburner motor 55.

If combustion is not established as a result of the energization of theignition device and burner motor, the combustion switch 25 will remainclosed and the electric heater 2| will remain energized. After apredetermined time (usually about 90 seconds) the bimetallic blade I 9of the safety switch will warp toward the right far.

enough to release the switch blades 29 and I9,

which will move under their bias to open circuit position. This willresult in the deenergization of the two relay windings 39 and 34 whichwill in turn deenergize the ignition device and burner motor. As setforth above, the safety switch can be returned to closed position onlyby the manual operation of the reset member 22.

Normally, however, the energization of the ignition device and burnermotor will result in the establishment of combustion. In response tocombustion,the switch 25 will move to open circuitposition which willresult in the deenergization of the safety switch heater 2| and relaywinding 39 which in turn will deenergize the ignition device 55. This isthe running condition When the room thermostat i9 is satisfied, it willcause the switch blade |2 to separate from contact l4 which willdeenergize the be ready for another normal start.

Assume now that combustion has been established and the systenris inrunning condition.

The combustion switch 25 will be open and the relay winding 39 andignition device 55 deener- ,gized. It is one of the main objects of theinvention to provide a system which will be shut failure and which willprevent. the reenergization of the burner motor and ignition deviceuntil after a manual operation has been per- I formed. The presentsystem accomplishes these results because if combustion should failduring a normal run, the combustion responsive switch 25 will firstreturn to closed position. This will as the relay winding 39 isenergized and pulls in ing 52.

result in connecting the safety switch heater 2| directly across thesecondary winding 52 by means of the following circuit: from one side ofthe secondary 52 through conductor 19, contact I4, switch blade l2,bimetallic element conductors 31 and 95, switch arm 41, contact 5|,conductors 91 and 92, switch arm 34, contact 31, conductors I93 and 14,switch blade 23, contact 21, conductor 15, heater 2|, conductors l5 and11, switch blades 29 and |9, and conductor 18 back to the other side ofthe secondary wind- It will be recalled that on an original call forheat the safety switch heater 2| was connected in series with the relaywinding 39. Now it will be noted that this heater is connected directlyacross the secondary winding 52 and therefore it will give off ,a muchgreater amount of heat at this time than on an original call for heatwith the result that the bimetallic blade l8 will release the safetyswitch blades 29 and I9 in a muchv shorter period of time than theninety second timing interval which must elapse before the system shutsdown on an original call for heat. After the switch blades 29 and I9have moved to open circuit position as a result of their bias, thesystem will be effectively deenergized and locked out and cannot bereenergized until the safety switch has been reset by the manual member22. will not recycle following a flame failure.

It will therefore be seen that I have provided a system in which thesafety switch shuts the system down after a flame failure and preventsrecycle wherein the safety switch timing is very much shorter followinga flame failure than it is upon an original call for heat.

Various changes and modifications of this system will doubtless occur tothose who are skilled safety switch, a heater therefor, a closed coldcombustion switch, a main switch, a source of power, a circuit for saidfirst relay winding indirectly across the source of power and includ-.

down as rapidly as possible following a flame eluding said main switch,combustion switch, heater, and source of power, a first switch closed bysaid first relay, a circuit for said second relay winding including saidmain switch and first switch, second and third switches closed by saidsecond relay, a circuit for said fuel feeding device including saidsecond switch, a holding circuit for said second relay winding includingsaid main switch and third switch, the opening of said combustion switchupon the establishment of combustion breaking the circuit for said firstrelay winding, and a circuit established by said combustion switch upona subsequent failure of combustion, said circuit connecting said heatering said main switch, third'switch, and combustion switch.

2. A fuel burner control system comprising in combination a fuel feedingdevice, a flrst relay having a first relay winding, a second relayhaving a second relay winding, a thermally timed safety switch, a heatertherefor, a closed cold combustion switch, a main switch, a source ofpower, first and second "out switches closed by In other words thissystem said first and second relays respectively when they aredeenergized, an energizing circuit for said first relay comprising saidmain switch, second "out switch, first relay winding, combustion switch,heater, and source of power, first and second in switches closed by saidfirst and second relays respectively when energized, an energizingcircuit for said second relayicomprising said mainswitch, first inswitch, second relay winding, and source of power, a holding circuit forsaid second relay including said main switch, second in switch, secondrelay winding, and source of power, a third in" switch closed by saidsecond relay when energized, a circuit for said fuel feeding deviceincluding said third "in switch, said combustion switch opening upon theestablishment of combustion to deenergize said first relay, and acircuit established upon a subsequent failure of combustion comprisingsaid main switch, second in switch, first out switch, combustion switch,heater, and source of power.

3. A fuel burner control system comprising in combination, a fuelfeeding device, a first relay having a first relay winding, a secondrelay having a second relay winding, a thermally timed safety switch, aheater therefor, a closed cold ing a relay winding, an "in" switchclosed by said relay when it is energized, and an "out" switch closed bysaid relay when it is deenergized; a thermally timed safety switch, aheater therefor; a closed cold combustion. switch; a main switch; asource of power; an energizing circuit for the winding of said relaycomprising said main switch, said combustion switch, heater, and saidsource of power; means controlled by said mainswitch and said. safetyswitch operative upon closure of said in switch to initiate energizationof said fuel feeding device and to combustion switch, a main switch, asource of I power, first and second out" switches closed by said firstand second relays respectively when they are deenergized, an energizingcircuit for said first relay comprising said main switch, second ,outswitch, first relay winding, combustion switch,-heater, and source ofpower, first and second in switches closed by said first and secondrelays respectively when energized, an energizing circuit for saidsecond relay comprising said main switch, first in switch, second relaywinding, and source of power, a holding circuit for said econd relayincluding said main switch, second in switch, second relay winding, andsource of power, a third in switch closed by said second relay whenenergized, a circuit for said fuel feeding device including said thirdin switch, said combustion switch opening upon the establishment ofcombustion to deenergize said first relay, a circuit established upon asubsequent failure of combustion comprising said main switch, second inswitch, first ou switch, combustion switch, heater, and source of power,and an intermittent ignition device for the fuel controlled by saidfirst relay.

4. A fuel burner control system comprising in combination; a fuelfeeding device; a relay havmaintain such energization independently ofsaid in" switch; and circuit means including said out switch and saidcombustion switch operative upon the reclosure of said combustion switchdue to flame failure following the deenergization of said relay as theresult of a previous establishment of combustion to cause said heater tobe connected substantially directly across said source of power andindependently of said relay winding.

5. A fuel burn-er control system comprising in combination; a fuelfeeding device; igniting means; a relay having a relay winding, firstand second in switches closed by said relay when it is energized, and anout" switch closed by said relay when it is deenergized; a thermallytimed safety switch, a heater therefor; a closed cold combustion switch;a main switch; a source of power; an energizing circuit for the windingof said relay comprising said main switch, said combustion switch,heater, and said source of power; means including one of said inswitches operative to cause operation of said ignition means duringclosure of said in switch; means con trolled by said main switch andsaid safety switch operative upon closure of the other in switch toinitiate energization of said fuel feeding device and to maintain suchenergization independently of said other in switch; said combustionswitch being operative upon initiation of combustion to open saidenergizing circuit for said relay and thereby to terminate operation ofsaid ignition means; and circuit means including said out switch andsaid combustion switch operative upon the reclosure of said combustionswitch due to flame failure following the deenergization of said relayas the result of a previous establishment of combustion to cause saidheater to be connected substantially directly across said source ofpower and independently of said relay winding.

ERNEST M. MILLER.

